paulears Posted July 10, 2008 Share Posted July 10, 2008 I've dropped a bit of a clanger. I bought a pile of camera cable, 2 50m drums and 2 100m drums. The camera connectors had been cut off, so for the use I had in mind, I've terminated the ends with breakout boxes, giving me composite and y/c , DC 13.8V, and a balanced XLR line. I tested the long ones with composite, looked an a scope, and concluded video was fine. The audio was easy, and the DC cores out and back on 100m were about 5.5 Ohms. I've miscalculated the volt drop - mainly because I didn't realise that with the viewfinders the current requirement was 1.7 Amps, leaving me with insufficient voltage to power up a camera. As a solution I'm considering some kind of voltage regulators at the camera end, and higher voltage power supplies, or variable voltage PSUs that I can just increase to something sufficient to overcome the 8V or so drop I have at the moment. If anyone has a better solution - I'd appreciate it! Link to comment Share on other sites More sharing options...
broadcast_techie Posted July 10, 2008 Share Posted July 10, 2008 What cable is it? How many cores?How many cores are you using for what?Could you combine cores to reduce the resistance..... Kris Link to comment Share on other sites More sharing options...
paulears Posted July 10, 2008 Author Share Posted July 10, 2008 It's very similar to Sony CQQ type:2 x 75ohm shielded coaxial, 2 conductors 16 AWG, 1x audio shielded twisted pair, 5 conductors 26 AWG So nothing really I can do, I'm using the two heaviest cores already, the 5 control cables are not in use, but are quite tiny. Thanks for the help. Link to comment Share on other sites More sharing options...
Lion Tamer Posted July 10, 2008 Share Posted July 10, 2008 If I was in your position I would go down the route of a voltage regulator with a couple of electolytic capacitors for some extra smoothing and a bridge rectifier so that you could connect your power supply either way round as an extra dgree of protection. My thoughts on the device if I was doing this going on the information provide would be to use an "L200" as it is capable of up to 2A output 40V input and can be configured easily to provide overcurrent and short circuit protection (it also has thermal protection inbuilt). Hope that helps Jem Link to comment Share on other sites More sharing options...
timmeh Posted July 10, 2008 Share Posted July 10, 2008 Hi I'd send 48v DC down it and rectify it at the other end. All the bestTimmeh Link to comment Share on other sites More sharing options...
themadhippy Posted July 10, 2008 Share Posted July 10, 2008 id try various parallel combination of both the 16 and 26 AWG cables before spending out on extra bits Link to comment Share on other sites More sharing options...
broadcast_techie Posted July 10, 2008 Share Posted July 10, 2008 An out of the box thought that I've not thought about in any depth: how about sending low volt AC? The more I do think about it it doesn't seem to help, but I may be wrong! Kris Link to comment Share on other sites More sharing options...
paulears Posted July 10, 2008 Author Share Posted July 10, 2008 The 200 is small enough to fit in the ali box with a bit of re-arrangement. Just a little agravating as I have plenty of perfectly serviceable 4 pin psus, which is what I'd assumed I was going to use, fitting 4 pins at both ends. I wonder if the old Sony CCUs with the cable compensator knob also increased the supply voltage when you selected the longer lengths? I always thought it was just eq, but maybe not? Not quite sure where I'd find a hefty 48V psu!Thanks all.p Link to comment Share on other sites More sharing options...
adamharman Posted July 10, 2008 Share Posted July 10, 2008 If it's dropping 8v from the 13.8, using the other cores in parallel isn't going to help that much.Higher voltage has to be the way to go, so the drop is less significant. A concurrent post has been automatically merged from this point on. Does it actually need to be as high as 48v? You need 13.8v, plus the 8v drop, plus whatever the minimum drop across the regulator is. I reckon 24v would just do it. Link to comment Share on other sites More sharing options...
Bobbsy Posted July 12, 2008 Share Posted July 12, 2008 When I had a vaguely similar problem a number of years back (wanting to power a couple of cameras from an SNG vehicle with no budget for proper CCUs/triax) the best we could come up with was to up the voltage from the on-truck power supply. This wasn't ideal because the voltage output was non-standard (around 18 volts if I recall) but got us through until the next budget year when we switched to proper triax. If you do go this route, I'd put some sort of non-standard connector on the source end so nobody can accidentally plug in a short length of ordinary camera cable and get a much higher voltage than expected. Bob Link to comment Share on other sites More sharing options...
Dmills Posted July 12, 2008 Share Posted July 12, 2008 One other comment:The screen of the coax is probably bonded to the negative supply terminal at the camera end (which from the sound of it is 4V above the power supply negative, if the power supply neg is common to anything video related at the supply end you may need to play some DC restoration games? Regards, Dan. Link to comment Share on other sites More sharing options...
boatman Posted July 12, 2008 Share Posted July 12, 2008 In a similar way to the National Grid distribution system, to minimise losses you need to start with the highest available voltage and use a very efficient converter at the remote end. As Timmeh said, 48VDC would probably be good, however rectifying it at the far end won't help much. For the lowest noise solution, look for a 48V to 12V DC/DC switch-mode converter and follow that with a linear regulator. The higher the starting voltage the lower the current and subsequent voltage losses in the cable will be. Link to comment Share on other sites More sharing options...
Simon Lewis Posted July 12, 2008 Share Posted July 12, 2008 Paul, I have a substantially engineered 48V psu, and might know where there's more... PM if you are interested! Simon Link to comment Share on other sites More sharing options...
Jivemaster Posted July 15, 2008 Share Posted July 15, 2008 Look at RS 248-120 it is an open frame psu with remote sensing. You have already gone away from standard connectors so use two of the spare lines as sense return lines. That way the intended voltage at the camera stays the same during load variations. Not saying that that particular part is the best but the idea seems the easiest way of getting a variable load powered. Link to comment Share on other sites More sharing options...
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